Method for formulating organic compounds

ABSTRACT

The present invention relates to a process for the formylation of organic compounds.

[0001] The present invention relates to a process for the formylation of organic compounds.

[0002] The formylation of suitable organic compounds is a process which is very frequently carried out in the chemical industry and whose great importance is also reflected in numerous publications on this subject.

[0003] However, carrying out formylations on an industrial scale is accompanied by safety problems and risks. Firstly, relatively large amounts of highly toxic chemical substances which themselves pose a considerable risk to human beings and the environment are frequently used and, secondly, formylations frequently proceed very exothermically so that there is an increased risk of explosion when carrying out these reactions on an industrial scale. Obtaining approval from the authorities under the German Federal Pollution Control Law for the operation of plants for the formylation of organic compounds on an industrial scale is therefore associated with a considerable outlay.

[0004] It is therefore an object of the present invention to provide a process for the formylation of organic compounds which avoids the abovementioned disadvantages. This process should, in particular, be able to be carried out in a simple, reproducible manner with increased safety for human beings and the environment and give good yields, and the reaction conditions should be very readily controllable.

[0005] This object is surprisingly achieved by the process of the invention for the formylation of organic compounds, in which at least one organic compound in liquid or dissolved form is mixed with at least one formylation reagent in liquid or dissolved form in at least one microreactor, reacts during a residence time and the formylated organic compound is, if desired, isolated from the reaction mixture.

[0006] For the purposes of the present invention, a formylation is a reaction in which an aldehyde group and/or a keto group is/are introduced into an organic compound.

[0007] Advantageous embodiments of the process of the invention are described in the subordinate claims.

[0008] According to the invention, individual organic compounds or mixtures of at least two of these compounds can be reacted by the process claimed. Preference is given to reacting only one organic compound by the process of the invention.

[0009] For the purposes of the invention, a microreactor is a reactor having a volume of ≦1000 μl in which the liquids and/or solutions are intimately mixed at least once. The volume of the microreactor is preferably ≦100 μl, particularly preferably ≦50 μl.

[0010] The microreactor is preferably made of thin, interconnected silicon structures.

[0011] The microreactor is preferably a miniaturized flow reactor, particularly preferably a static micromixer. The microreactor is very particularly preferably a static micromixer as described in the Patent Application WO 96/30113, which is hereby incorporated by reference into the present disclosure. Such a micromixer has small channels in which liquids and/or chemical compounds present in solutions are mixed with one another by means of the kinetic energy of the flowing liquids and/or solutions.

[0012] The channels of the microreactor preferably have a diameter of from 10 to 1000 μm, particularly preferably from 20 to 800 μm and very particularly preferably from 30 to 400 μm.

[0013] The liquids and/or solutions are preferably pumped into the microreactor so that they flow through the latter at a flow rate of from 0.01 μl/min to 100 ml/min, particularly preferably from 1 μl/min to 1 ml/min.

[0014] According to the invention, the microreactor can preferably be heated and cooled.

[0015] The microreactor is, according to the invention, preferably connected via an output to at least one residence section, preferably a capillary, particularly preferably a heatable/coolable capillary. After they have been mixed in the microreactor, the liquids and/or solutions are passed through this residence section or capillary to increase their residence time.

[0016] For the purposes of the invention, the residence time is the time between the mixing of the starting materials and the work-up of the resulting reaction solution for analysis or isolation of the desired product(s).

[0017] The residence time necessary in the process of the invention depends on various parameters such as the temperature or the reactivity of the starting materials. A person skilled in the art can match the residence time to these parameters and thus achieve optimized reaction conditions.

[0018] The residence time of the reaction solution in the system employed comprising at least one microreactor and, if desired, one residence section can be set by choice of the flow rate of the liquids and/or solutions used.

[0019] It is likewise preferred for the reaction mixture to be passed through two or more microreactors connected in series. This increases the residence time even in the case of an increased flow rate and results in the components used in the formylation reaction being reacted so that an optimum product yield of the desired formylated organic compound(s) is achieved.

[0020] In a further, preferred embodiment, the reaction mixture is passed through two or more microreactors connected in parallel so as to increase the throughput.

[0021] In another preferred embodiment of the process of the invention, the number and arrangement of the channels is varied in one or more microreactor(s) so as to increase the residence time, so that an optimum yield of the desired formylated organic compound(s) is also achieved here at an increased flow rate.

[0022] The residence time of the reaction solution in the microreactor or if applicable in the microreactor and the residence section is preferably ≦15 hours, preferably ≦3 hours, particularly preferably ≦1 hour.

[0023] The process of the invention can be carried out within a very wide temperature range which is limited essentially by the temperature stability of the materials used for the construction of the microreactor, any residence section and further components such as connections and seals and by the physical properties of the solutions and/or liquids used. The process of the invention is preferably carried out at a temperature of from −100 to +250° C., preferably from −78 to +150° C., particularly preferably from 0 to +100° C.

[0024] The process of the invention can be carried out either continuously or batchwise. It is preferably carried out continuously.

[0025] To carry out the process of the invention for the formylation of organic compounds, it is necessary for the formylation reaction to be carried out, if possible, in a homogeneous liquid phase containing no solid particles or only very small solid particles, since otherwise the channels in the microreactors become blocked.

[0026] The course of the formylation reaction in the process of the invention can be followed by means of various analytical methods known to those skilled in the art and if necessary regulated. The course of the reaction is preferably followed chromatographically, particularly preferably by high-pressure liquid chromatography, and regulated if necessary. The control of the reaction is significantly improved compared with known processes.

[0027] After the reaction, the formylated organic compound(s) is (are) isolated if desired. The formylated organic compound(s) is (are) preferably isolated from the reaction mixture by extraction.

[0028] As organic compounds, it is possible for all organic compounds known to those skilled in the art as substrates for formylations to be used in the process of the invention. The organic compounds are preferably selected from among olefins, alkynes, aromatic compounds, heteroaromatic compounds, transition metal complexes, CH-acid compounds, enamides and mixtures of at least two of these compounds.

[0029] As olefins, it is possible to use all olefins known to those skilled in the art which are suitable as substrates for formulations. These encompass straight-chain, branched and cyclic olefins. Preference is given to using unsubstituted or substituted ethylene as olefin.

[0030] As alkynes, it is possible to use all alkynes known to those skilled in the art which are suitable as substrates for formylations. These encompass straight-chain, branched and cyclic alkynes. Preference is given to using substituted acetylene as alkyne.

[0031] As aromatic compounds, it is possible to use all aromatic compounds known to those skilled in the art which are suitable as substrates for formulations. For the purposes of the invention, these include compounds and/or derivatives which have a monocyclic and/or polycyclic homoaromatic framework or a corresponding substructure, e.g. in the form of substituents. As aromatic compound, which may be substituted or unsubstituted, preference is given to using azulene, indole, phenol, an aromatic amine or a mixture of at least two of these compounds.

[0032] As heteroaromatic compounds, it is possible to use all heteroaromatic compounds known to those skilled in the art which are suitable as substrates for formylations and have at least one heteroatom. For the purposes of the invention, heteroaromatic compounds include heteroaromatic compounds and/or their derivatives which have at least one monocyclic and/or polycyclic heteroaromatic framework or a corresponding substructure, e.g. in the form of substituents. These heteroaromatic frameworks or substructures preferably include at least one oxygen, nitrogen and/or sulfur atom. As heteroaromatic compounds, which may be substituted or unsubstituted, particularly preference is given to using furan, thiophene, pyrrole, benzofuran, benzothiophene, pyrazole, imidazole, thiazole, oxazole, pyrimidine, porphyrin, hydantoin, thiohydantoin, imidazolone, pyrazolone or a mixture of at least two of these compounds.

[0033] As transition metal complexes, it is possible to use all transition metal complexes known to those skilled in the art which are suitable as substrates or formylations. For the purposes of the invention, transition metal complexes include, inter alia, metallocene compounds, preferably ferrocene, and carbonyl compounds of the transition metals, preferably carbonyl compounds of iron, chromium or manganese and mixtures of at least two of these compounds.

[0034] As CH-acid compounds, it is possible to use all CH-acid compounds known to those skilled in the art which are suitable as substrates for formylations and have at least one acid proton in the α position relative to a carbonyl group. As CH-acid compound, preference is given to using an enol, an enol ether, a β-keto compound, particularly preferably pyrazole-3,5-dione, or a mixture of at least two of these compounds.

[0035] As enamides, it is possible to use all enamides known to those skilled in the art which are suitable as substrates for formylations. As enamide, preference is given to using a vinylic formamide, particularly preferably 3-dimethylaminopropenal.

[0036] Formylation reagents which can be used in the process of the invention are all formylation reagents known to those skilled in the art which are suitable for formylations and mixtures of at least two of these reagents. Preference is given to using only one formulation reagent in each case. For the purposes of the invention, formulation reagents also include formylation reagents formed in situ, i.e. formylation reagents which are formed immediately before or during the formylation reaction.

[0037] In a further, preferred embodiment of the invention, the formulation reagent used is an N,N-disubstituted formamide, an N-alkylformanilide, an N,N-disubstituted amide or a mixture of at least two of these compounds in the presence of an inorganic acid chloride, an inorganic ester, an acid anhydride, an adduct of triphenylphosphine and bromine, cyanuric chloride, hexachlorocyclotriphosphazane or a mixture of at least two of the abovementioned compounds.

[0038] As N,N-disubstituted formamide, preference is given to using an N-aryl-N-alkylformamide, particularly preferably N-phenyl-N-methylformamide, an N,N-dialkyl formamide, particularly preferably N,N-dimethylformamide, a vinylic N,N-dialkylformamide or a mixture of at least two of these compounds.

[0039] As N-alkylformanilide, preference is given to using an N-methylformanilide.

[0040] As N,N-disubstituted amide, preference is given to using an N,N-dialkylacetamide, particularly preferably N,N-dimethylacetamide, an N,N-dialkyl propionamide, particularly preferably N,N-dimethylpropionamide, an N,N-dialkylbenzamide, preferably N,N-dimethylbenzamide, or a mixture of at least two of these compounds.

[0041] As inorganic acid chloride, preference is given to using phosphorus oxychloride, thionyl chloride, phosgene, a phosgene substitute, in particular diphosgene or triphosgene, pyrophosphoryl chloride, oxalyl chloride, sulfuryl chloride, benzoyl bromide or a mixture of at least two of these compounds.

[0042] As acid anhydride, preference is given to using trifluoromethanesulfonic anhydride.

[0043] As inorganic ester, preference is given to using a dialkyl sulfate, particularly preferably dimethyl sulfate.

[0044] The molar ratio of N,N-disubstituted formamide and/or N-alkylformanilide and/or N,N-disubstituted amide to inorganic acid chloride and/or inorganic ester and/or acid anhydride is preferably equimolar. Furthermore, the acid chloride and/or the inorganic ester and/or the acid anhydride is/are preferably present in a 2-fold to 10-fold molar excess, particularly preferably in a 3-fold to 5-fold molar excess, based on the N,N-disubstituted formamide and/or the N-alkylformanilide and/or the N,N-disubstituted amide.

[0045] In a further, preferred embodiment of the process of the invention, the formylation reagent used is zinc(II) cyanide in the presence of a protic acid, preferably hydrochloric acid.

[0046] The molar ratio of organic compound to formylation reagent used in the process of the invention depends on the reactivity of the organic compound used and the reactivity of the formylation reagent used. The formylation reagent and the organic compound are preferably used in an equimolar ratio. In another preferred embodiment of the process of the invention, the formylation reagent is used in a 2-fold to 20-fold molar excess, particularly preferably in a 3-fold to 15-fold excess, very particularly preferably in a 4-fold to 10-fold excess, based on the organic compound.

[0047] The selectivity of the reaction itself depends not only on the concentration of the reagents used but also on a series of further parameters such as the temperature, the type of formylation reagent used or the residence time. A person skilled in the art will be able to match the various parameters to the respective formylation so that the desired formylation product(s) is (are) obtained.

[0048] It is important for the process of the invention that the organic compounds used and the formylation reagents used are either themselves liquid or are in dissolved form. If they are themselves liquid, they can, if desired, also be used as solvents for further components of the formylation reaction. If the organic compounds or formylation reagents used are not themselves in liquid form, they have to be dissolved in a suitable solvent before carrying out the process of the invention. Solvents used are preferably halogenated solvents, particularly preferably dichloromethane, chloroform, 1,2-dichloroethane or 1,1,2,2-tetrachloroethane, straight-chain, branched or cyclic paraffins, particularly preferably pentane, hexane, heptane, octane, cyclopentane, cyclohexane, cycloheptane or cyclooctane, or straight-chain, branched or cyclic ethers, particularly preferably diethyl ether, methyl tert-butyl ether, tetrahydrofuran or dioxane, aromatic solvents, particularly preferably toluene, xylenes, ligroin or phenyl ether, N-containing solvents, particularly preferably N,N-dimethylformamide or N-methylpyrrolidone, or mixtures of at least two of the abovementioned solvents.

[0049] In the process of the invention, the danger to human beings and the environment due to loss of containment of chemicals is considerably reduced and thus leads to increased safety when handling hazardous substances. Furthermore, the formylation of organic compounds by the process of the invention makes it possible for the reaction conditions, e.g. reaction time and reaction temperature, to be controlled better than is possible in the conventional processes. In addition, the risk of explosions in the case of very strongly exothermic formulations is significantly reduced in the process of the invention. The temperature can be selected individually and kept constant in each volume element of the system. In the process of the invention, the formylation reactions are very fast and can be regulated precisely. The formylated organic compounds can thus be obtained in very good and reproducible yields.

[0050] It is also particularly advantageous that the process of the invention can be carried out continuously. As a result, it is faster and cheaper than conventional processes and it is possible to prepare any amounts of the formylated organic compounds without a great outlay in terms of instrumentation.

[0051] The invention is illustrated below by means of an example. This example serves merely to illustrate the invention and does not restrict its scope.

EXAMPLE Formylation of Indole to Give indole-3-carboxaldehyde

[0052] The formylation of indole by means of N,N-dimethylformamide in the presence of phosphorus oxychloride was carried out in a static micromixer (Technische Universität Ilmenau, Fakultät Maschinenbau, Dr.-Ing. Norbert Schwesinger, Postfach 100565, D-98684, Ilmenau) having a size of 40 mm×25 mm×1 mm and a total of 11 mixing stages each having a volume of 0.125 μl. The total pressure drop was about 1000 Pa. The static micromixer was connected via an outlet and an Omnifit intermediate-pressure HPLC connector (Omnifit, Great Britain) to a Teflon capillary having an internal diameter of 0.49 mm and a length of 1.0 m. The reaction was carried out at 0° C. and 25° C. The static micromixer and the Teflon capillary were for this purpose maintained at the respective temperature in a thermostated double-walled vessel.

[0053] A 2 ml disposable syringe was filled with part of a solution of 0.78 ml (8.5 mmol) of phosphorus oxychloride and 20 ml of N,N-dimethylformamide, which simultaneously serves as solvent, and a further 2 ml disposable syringe was filled with part of a solution of 1 g (8.5 mmol) of indole in 20 ml of N,N-dimethylformamide. The contents of both syringes were subsequently transferred by means of a metering pump (Harvard Apparatus Inc., Pump 22, South Natick, Mass., USA) into the static micromixer. Before carrying out the reaction, the test apparatus was calibrated to determine the dependence of the residence time on the pump flow rate. The residence time was set to 1.88; 3.75; 7.5; 15 and 30 minutes. The reactions were followed with the aid of a Merck Hitachi LaChrom HPLC instrument. The ratio of starting material to product corresponding to the respective reaction conditions and residence times was also determined by means of HPLC on the abovementioned instrument. 

1. Process for the formylation of organic compounds, characterized in that at least one organic compound in liquid or dissolved form is mixed with at least one formylation reagent in liquid or dissolved form in at least one microreactor, reacts during a residence time and the formylated organic compound is, if desired, isolated from the reaction mixture.
 2. Process according to claim 1, characterized in that the microreactor is a miniaturized flow reactor.
 3. Process according to claim 1 or 2, characterized in that the microreactor is a static micromixer.
 4. Process according to any of claims 1 to 3, characterized in that the microreactor is connected via an outlet to a capillary, preferably a capillary which can be heated and cooled.
 5. Process according to any of claims 1 to 4, characterized in that the volume of the microreactor is ≦100 μl, preferably ≦50 μl.
 6. Process according to any of claims 1 to 5, characterized in that the microreactor can be heated and cooled.
 7. Process according to any of claims 1 to 6, characterized in that the microreactor has channels having a diameter of from 10 to 1000 μm, preferably from 20 to 800 μm, particularly preferably from 30 to 400 μm.
 8. Process according to any of claims 1 to 7, characterized in that the reaction mixture flows through the microreactor at a flow rate of from 0.01 μl/min to 100 ml/min, preferably from 1 μl/min to 1 ml/min.
 9. Process according to any of claims 1 to 8, characterized in that the residence time of the compounds used in the microreactor or in the microreactor and the capillary is ≦15 hours, preferably ≦3 hours, particularly preferably ≦1 hour.
 10. Process according to any of claims 1 to 9, characterized in that it is carried out at a temperature of from −100 to +250° C., preferably from −78 to +150° C., particularly preferably from 0 to +100° C.
 11. Process according to any of claims 1 to 10, characterized in that the course of the reaction is followed chromatographically, preferably by high-pressure liquid chromatography, and is regulated if appropriate.
 12. Process according to any of claims 1 to 11, characterized in that the formylated organic compound is isolated from the reaction mixture by extraction.
 13. Process according to any of claims 1 to 12, characterized in that the formylation reagent used is an N,N-disubstituted formamide, an N-alkylformanilide, an N,N-disubstituted amide or a mixture of at least two of these compounds in the presence of an inorganic acid chloride, an inorganic ester, an acid anhydride, an adduct of triphenylphosphine and bromine, cyanuric chloride, hexachlorocyclophosphazane or a mixture of at least two of these compounds.
 14. Process according to claim 13, characterized in that an N-aryl-N-alkylformamide, preferably an N-phenyl-N-methylformamide, an N,N-dialkylformamide, preferably N,N-dimethylformamide, a vinylic N,N-dialkylformamide or a mixture of at least two of these compounds is used as N,N-disubstituted formamide.
 15. Process according to claim 13 or 14, characterized in that N-methylformanilide is used as N-alkylformanilide.
 16. Process according to any of claims 13 to 15, characterized in that an N,N-dialkylacetamide, preferably N,N-dimethylacetamide, an N,N-dialkyl propionamide, preferably N,N-dimethylpropionamide, an N,N-dialkylbenzamide, preferably N,N-dimethylbenzamide, or a mixture of at least two of these compounds is used as N,N-disubstituted amide.
 17. Process according to any of claims 13 to 16, characterized in that phosphorus oxychloride, thionyl chloride, phosgene, a phosgene substitute, preferably diphosgene or triphosgene, pyrophosphoryl chloride, oxalyl chloride, sulfuryl chloride, benzoyl chloride or a mixture of at least two of these acid chlorides is used as inorganic acid chloride.
 18. Process according to any of claims 13 to 17, characterized in that a dialkyl sulfate, preferably dimethyl sulfate, is used as inorganic ester.
 19. Process according to any of claims 13 to 18, characterized in that trifluoromethanesulfonic anhydride is used as acid anhydride.
 20. Process according to any of claims 13 to 19, characterized in that the molar ratio of N,N-disubstituted formamide and/or N-alkylformanilide and/or N,N-disubstituted amide to inorganic acid chloride and/or inorganic ester and/or acid anhydride is equimolar, or in that the inorganic acid chloride and/or the inorganic ester and/or the acid anhydride is/are used in a 2-fold to 10-fold polar excess, preferably in a 3-fold to 5-fold molar excess, based on the N,N-disubstituted formamide and/or the N-alkylformanilide and/or the N,N-disubstituted amide.
 21. Process according to any of claims 1 to 12, characterized in that the formylation reagent used is zinc(II) cyanide in the presence of a protic acid, preferably hydrochloric acid.
 22. Process according to any of claims 1 to 21, characterized in that the organic compound used is an olefin, an alkyne, an aromatic compound, a heteroaromatic compound, a transition metal complex, a CH-acid compound, an enamide or a mixture of at least two of these compounds.
 23. Process according to claim 22, characterized in that unsubstituted or substituted ethylene is used as olefin.
 24. Process according to claim 22 or 23, characterized in that unsubstituted or substituted acetylene is used as alkyne.
 25. Process according to any of claims 22 to 24, characterized in that azulene, indole, phenol, an aromatic amine or a mixture of at least two of these compounds is used as aromatic compound, which may be unsubstituted or substituted.
 26. Process according to any of claims 22 to 25, characterized in that a metallocene, preferably ferrocene, a carbonyl compound of a transition metal, preferably a carbonyl compound of iron, chromium or manganese, or a mixture of at least two of these compounds is used as transition metal complex.
 27. Process according to any of claims 22 to 26, characterized in that furan, thiophene, pyrrole, benzofuran, benzothiophene, pyrazole, imidazole, thiazole, oxazole, pyrimidine, porphyrin, hydantoin, thiohydantoin, imidazolone, pyrazolone or a mixture of at least two of these compounds is used as heteroaromatic compound, which may be unsubstituted or substituted.
 28. Process according to any of claims 22 to 27, characterized in that an enol, an enol ether or a β-keto compound, preferably pyrazole-3,5-dione, or a mixture of at least two of these compounds is used as CH-acid compound.
 29. Process according to any of claims 22 to 28, characterized in that a vinylic formamide, preferably 3-dimethylaminopropenal, is used as enamide.
 30. Process according to any of claims 1 to 29, characterized in that the molar ratio of organic compound to formylation reagent is equimolar, or in that the formylation reagent is used in a 2-fold to 20-fold molar excess, preferably in a 3-fold to 15-fold excess and particularly preferably in a 4-fold to 10-fold excess, based on the organic compound. 